Improve room list performance when receiving messages
In summary this makes RoomTiles (and RoomAvatars) do more for
themselves in terms of reacting individually to state changes in
the js-sdk.
Instead of force updating the entire room list for avatar changes
and room name changes, do this in the RoomTile and RoomAvatar
instead. This increases the number of listeners listening to the
matrix client, but allows us to properly implement a
shouldComponentUpdate for RoomTile (because the avatar, name and
notification count are now in component state)
